Project Summary Anorexia nervosa (AN) is a serious mental illness that confers the highest mortality rate of any psychiatric disorder. Current treatments are inadequate and no pharmacologic agents have proven effective. A better understanding of the development and pathophysiology of AN is greatly needed. We propose a longitudinal, multimodal MRI study of reward and habit circuits in youth (ages 14-18) with AN, compared with age-matched healthy controls (HC), followed over two years. We focus on adolescence because this is a critical, yet understudied, period in AN. Pathological dieting typically emerges during adolescence, and the course of AN is often determined during this period with approximately half of teens showing full recovery, whereas the rest endure persistent illness. Understanding the neurobiological mechanisms by which some teens develop persistent AN, while others remit, is critical to developing the most effective interventions. Our study will examine neural mechanisms guiding food choice and neural connectivity in mesolimbic and habit-related circuits among youth with AN who continue with illness compared with those who remit, and compared with HC. We will examine these neural circuits at baseline and study their developmental trajectories. Our Food Choice Task captures restrictive intake, a core behavioral disturbance in AN, and therefore we can directly examine the link between brain activity and eating behavior. Using longitudinal, multimodal MRI at 3- time points, we will first test whether the function and connectivity of mesolimbic reward and dorsal habit circuits predict the longer-term course of AN. Second, we will examine longitudinal changes within these two neural circuits of interest. We predict that at baseline, restrictive food choice in youth with AN will be mediated by mesolimbic reward circuitry; however, at year-2 follow-up, in teens for whom the disorder persists, restrictive food choice will be mediated by dorsal striatal habit circuitry. The study will (i) chart the developmental trajectories of reward and habit circuits in youth with AN; (ii) advance our understanding of the mechanisms by which AN persists to chronicity, and (iii) help develop targets for novel therapeutic strategies.